1. Field of the Invention
This invention relates to the use of specific zirconium salts in residual fuel oil to reduce the amount of particulate matter formed during combustion.
2. Brief Description of the Prior Art
Residual fuel oils, including Grades Nos. 4, 5 and 6 (ASTM D-396), are widely used in a variety of industrial heating and steam boiler applications. A particularly desired fuel oil is No. 6, which is extensively used by utility and power companies.
State and federal EPA emission standards are currently limiting the use of residual fuels which produce excessive amounts of particulate emission during combustion and thus are not in compliance with standards.
However, the situation is relatively complicated, since state-to-state emission standards tend to be different and compliance by a residual fuel oil in one state may not necessarily be achieved in another, and further, since standards are continuously subject to change, a fuel oil currently in compliance may not be in compliance in the near future in the same location and under the same end-use conditions.
Fuels which tend to produce excessive amounts of particulate emission generally have one or more characteristics associated with them: a sulfur content above about 1 percent; a Conradson Carbon Residue (ASTM D-189, also termed "Con Carbon" in the art) above about 7 percent; or a high asphaltene content. Fuels yielding particulate emissions that surpass the existing standards can't be directly used, but in some cases can be blended in admixture with fuels that do meet existing standards, which are generally low in sulfur and/or low in "Con Carbon" and asphaltene content. This situation has resulted in an overall increased demand for fuel oils which meet emission standards despite their diminishing supply and attendant increase in cost.
What is desired is a process for increasing the utility of these high emission yielding residual fuel oils for industrial heating purposes in a manner that results in acceptable particulate emissions, despite a high sulfur content and/or a high Con Carbon residue.
In the area of related problems, it is known in the art that the use of specific additives in certain hydrocarbon fuels, can reduce smoke or soot upon combustion, in certain instances.
U.S. Pat. No. 3,594,138 describes the use of metal salts of alkanoic acids, particularly Group IIA metal salts, for reducing soot and smoke produced upon combustion of hydrocarbon fuels used in compression and spark ignition engines. Preferred are barium and calcium salts of alkanoic acids and particularly preferred is the combination of said salt with an ether, such as ethylene glycol monomethyl ether. Zirconium salts are also mentioned.
U.S. Pat. No. 2,086,775 discloses a process for increasing the efficiency of internal combustion engines by the addition of organometallic compounds, including beta-diketone derivatives of cobalt, nickel, manganese, iron, copper, uranium, molybdenum, vanadium, zirconium, beryllium, platinum, palladium, chromium, aluminum, thorium, and the rare earth metals. Metals having special value are described as being beta-diketonates of cobalt, nickel, iron, copper and manganese.
U.S. Pat. No. 2,197,498 discloses the stabilization of hydrocarbon motor fuels containing dissolved organometallic compounds by the addition of an oil or water-soluble organic acid to prevent precipitation thereof. Included among sixteen metals mentioned, including rare earth metals, are zirconium organometallic compounds.
However, none of the above-described references disclose the effectiveness of specific additives in reducing particulate emission during combustion of specifically residual fuel oil, and particularly No. 6 fuel oil.
U.S. Pat. Nos. 3,205,053 and 3,231,592 describe metal oxide-fatty acid complexes which are useful as additives in residual fuel oils containing vanadium and sulfur in which the complex functions to reduce boiler corrosion by converting molten vanadium compounds to a high melting vanadate ash that can be exhausted. However, use of the described metal oxide-fatty acid complex, in which zirconium oxide is mentioned along with fifteen other metal oxides, including rare earth metal oxides, operates to increase the level of particulate emission. Further, the described complex generally requires two different metals and is generally insoluble in the residual oil and must be dispersed therein by means of dispersing agents.
We have unexpectedly found that by adding a zirconium salt of a fatty acid, tall oil or naphthenic acid, to a residual fuel oil, and particularly No. 6 fuel oil, the amount of particulate matter formed during combustion can be reduced in an amount of about 10 to 50 percent or greater. Particularly surprising is that the described zirconium salt is effective when used specifically with No. 6 fuel oil, whereas the same acid salts with other metals, for example, barium and magnesium, which are described in the art as being effective in reducing smoke or soot in the combustion of certain hydrocarbon fuel oils, were found to be ineffective in this particular application.
In accordance with this invention, there is provided a process for reducing the amount of particulate matter formed during the combustion of a residual fuel oil comprising the steps of:
(a) dissolving in said fuel oil an effective trace amount of an additive consisting essentially of a zirconium salt of a carboxylic acid selected from the group consisting of C.sub.4 -C.sub.22 linear or branched fatty acids, tall oil, naphthenic acid, or mixtures thereof, said amount being effective in reducing the amount of particulate matter formed during combustion as compared to said process conducted in the absence of said zirconium salt; and
(b) combusting said resulting fuel oil.
Further provided is a composition comprising a residual fuel oil having dissolved therein an effective trace amount of an additive consisting essentially of a zirconium salt of a carboxylic acid, selected from the group consisting of C.sub.4 -C.sub.22 linear or branched fatty acids, tall oil, naphthenic acid or mixtures thereof, said amount being effective in reducing the amount of particulate matter formed during combustion of said fuel oil.
Preferred embodiments of the above-described process and composition are where the residual fuel oil is No. 6 fuel oil, the zirconium additive is zirconium octanoate, present in said fuel oil in about 10-1000 ppm by weight, taken as the metal.